Technical Field
This technology relates to fishing lines made from high tenacity polyolefin fibers and processes for making the lines.
Description of the Related Art
Fibers formed from ultra high molecular weight polyethylene (UHMW PE) are known to possess excellent tensile properties such as tenacity, tensile modulus and energy-to-break. Such high tenacity fibers are typically made by a “gel spinning” process, also referred to as “solution spinning.” In this type of process, a solution of ultra high molecular weight polyethylene (UHMW PE) and a solvent is formed, followed by extruding the solution through a multi-orifice spinneret to form solution filaments, cooling the solution filaments into gel filaments, and extracting the solvent to form dry filaments. These dry filaments are grouped into bundles which are referred to in the art as either “fibers” or “yarns.” The fibers/yarns are then stretched (drawn) up to a maximum drawing capacity to increase their tenacity.
The preparation of high strength polyethylene filaments and/or multi-filament fibers/yarns has been described for example in U.S. Pat. Nos. 4,411,854; 4,413,110; 4,422,993; 4,430,383; 4,436,689; 4,455,273; 4,536,536; 4,545,950; 4,551,296; 4,584,347; 4,663,101; 5,248,471; 5,578,374; 5,736,244; 5,741,451; 5,972,498; 6,448,359, 6,969,553; 7,078,097; 7,078,099; 7,081,297; 7,115,318; 7,344,668; 7,638,191; 7,674,409; 7,736,561; 7,846,363; 8,070,998; 8,361,366; 8,444,898; 8,506,864; and 8,747,715. Each of these inventions provides incremental improvements in UHMW PE processing technology and illustrates the great difficulty in improving the tensile properties of UHMW PE fibers. For example, while the tenacity and tensile modulus of UHMW PE fibers are increased by stretching (drawing) the fibers, they can only be stretched to a certain extent without breaking. The maximum amount that a fiber can be stretched, and thus the maximum tenacity that can be achieved for a particular fiber type, depends on several factors, including both improved raw materials and processing capabilities.
To maximize fiber tenacity, the polyethylene solution and its precursors (i.e. the polymer and solvent forming the solution) must have certain properties, such as a high intrinsic viscosity (“IV”), and must be made in a particular manner. For example, U.S. Pat. No. 8,444,898 teaches processes for producing high tenacity fibers by a specialized process that requires first forming a polyethylene solution by: a) forming a slurry of UHMW PO particles in a solvent; b) processing the slurry through an extruder at a throughput rate of at least the quantity 2.5 D2 (2.5×D×D) grams per minute, where D represents the screw diameter of said extruder in centimeters, to form a non-solution mixture in the extruder wherein the mixture contains domains of molten polymer and solvent having sizes of microscopic dimensions; c) discharging said non-solution mixture from the extruder; and d) passing said mixture through a heated vessel which provides the necessary residence time to convert the mixture to a homogeneous solution of UHMW PO dissolved in the solvent. This process is distinguished from a method where a homogenous solution is formed in the extruder, because the extruder exerts a shear stress upon the mixture that reduces the maximum achievable fiber tenacity. The thus formed solution is then passed through a shaping orifice to form a molded solution article, which is then stretched and cooled to obtain a molded gel article. The molded gel article is then stretched, followed by removing the solvent from the molded gel article to form a solid fiber, with additional stretching of the fiber being performed to increase the tenacity of the fiber to 40 g/denier or more.
U.S. Pat. No. 8,747,715 teaches a process for producing high tenacity polyethylene yarns wherein fibers are highly oriented to form a product having a tenacity of greater than about 45 g/d and a tensile modulus of greater than about 1400 g/d. The process involves passing a solution of ultra high molecular weight polyethylene in a solvent through a spinneret to form a solution yarn; drawing the solution yarn that issues from the spinneret to form a drawn solution yarn; cooling the drawn solution yarn to form a gel yarn; drawing the gel yarn; removing the solvent from the gel yarn to form a dry yarn; drawing the dry yarn to form a partially oriented yarn having an intrinsic viscosity of greater than about 19 dl/g; and drawing the partially oriented yarn to form a highly oriented yarn product having a tenacity of greater than about 45 g/d and a modulus of greater than about 1400 g/d. These are just two methods that exemplify the significant investment in science and technology that goes into even incremental improvements in the tensile properties of polyethylene fibers.
These processes produce fibers, commercially available from Honeywell International Inc. of Morristown, N.J. under the trademark SPECTRA®, that ounce-for-ounce are fifteen times stronger than steel while also light enough to float on water. Due to this excellent strength to weight ratio, SPECTRA® fibers are highly desirable for the manufacture products requiring impact absorption and ballistic resistance such as body armor, helmets, breast plates and spall shields, as well as composite sports equipment. They have also been used in other non-impact related applications, such as fishing lines, with commercial success.
Fishing lines comprising multifilament gel spun polyethylene fibers are typically made by braiding together a plurality of fibers. These multi-fiber, multi-filament fishing lines have superior strength compared to monofilament fishing lines formed from other polymers, such as polyesters or nylons, so they have a lower tendency to break during use. Due to their superior strength, braided fishing lines may be fabricated with lower line diameters relative to monofilament fishing lines having the same strength. This is significant, for example, because thinner lines allow anglers to cast longer and load more line onto their rod spool compared to monofilament lines. Braided fishing lines are also preferable because they are more durable than monofilament lines and thus will last longer without breaking down due to the sun or heavy use, and they have less of a tendency to coil and tangle than monofilament line. Furthermore, the braided, multi-fiber, multifilament construction is preferable to monofilament fishing lines because the monofilament line types have a tendency to stretch during use, whereas the braided lines do not stretch or have very little stretch. In this regard, non-stretching or low stretch lines are often preferred over greater stretch lines because they give anglers a better feel when they have a bite on their hook and they make it easier to set the hook after a bite.
Despite the existing high performance of braided fishing lines, there is an ongoing need for products having improved properties and performance. In particular, there is an ongoing need in the art for braided lines having lower diameters without sacrificing line strength. The present technology provides a solution to this need in the art, converting the very high tenacity SPECTRA® fibers, such as those manufactured according to processes described in U.S. Pat. Nos. 8,444,898 and 8,747,715, into high performance fishing lines having a greater breaking strength to diameter ratio than any other fishing line heretofore known in the art.